Warm white light emitting apparatus and back light module comprising the same

ABSTRACT

A warm white light emitting apparatus includes a first light emitting diode (LED)-phosphor combination to generate a base light that is white or yellowish white and a second LED-phosphor combination to generate a Color Rendering Index (CRI) adjusting light. The base light and the CRI adjusting light together make a warm white light having a color temperature of 2500 to 4500K.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/324,091 filed Nov. 26, 2008 and claims priority from and the benefitof Korean Patent Application No. 10-2008-0074113, filed on Jul. 29,2008, and Korean Patent Application No. 10-2008-0112863, filed on Nov.13, 2008, which are both hereby incorporated by reference for allpurposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relates to a warm whitelight emitting apparatus, and more particularly, to a warm white lightemitting apparatus that includes is an LED-phosphor combination togenerate a base light of white or yellowish white and an LED-phosphorcombination to generate light to adjust a Color Rendering Index (CRI) ofthe base light.

2. Discussion of the Background

A white light emitting apparatus using light emitting diodes (LEDs) aslight sources to emit white light has been increasingly developed. AnLED includes a junction of p-type and n-type semiconductors and uses alight emitting semiconductor in which energy corresponding to a bandgapof the semiconductor is emitted in the form of light due to arecombination of electrons and holes when voltage is applied thereto.

A white light emitting apparatus to emit white light using LEDs of threeprimary colors, i.e., red, green, and blue, is known. The white lightemitting apparatus, however, may have a complicated circuitconfiguration, may make it difficult to provide uniform white light dueto the difference of distances between the LEDs of the three primarycolors, and may not be economically efficient. Further, in the whitelight emitting apparatus using the LEDs of the three primary colors,color rendering and color reproduction properties of white light may belimited.

FIG. 16 is a Commission on Illumination (CIE) 1931 chromaticity diagramshowing full colors of a conventional white light emitting apparatus.Referring to FIG. 16, a triangle region defined by color coordinates ofthree primary colors used in the NTSC regulations exists on the CIE 1931chromaticity diagram. Light of a white region may be provided dependingon a change in slope of a curve according to current applied to red (R),green (G), and blue (B) LEDs in the triangle region. At this time, thewhite region is shown along a is black body locus curve (BBL curve),wherein the slope of the BBL curve increases from infinity to about4000K and then decreases after it passes through about 4000K, based on xand y axes that are the abscissa and the ordinate, respectively.Therefore, light of a warm white region that is shown along the BBLcurve and has an excellent color rendering property may not be providedusing only the red, green, and blue LEDs.

There is also known a white light emitting apparatus that emits whitelight using the combination of a blue LED and a yellow phosphor. Such awhite light emitting apparatus advantageously may provide a simplecircuit configuration and may be inexpensive. However, its colorrendering property may be degraded, and its color production propertymay be considerably degraded due to a low light intensity in a longwavelength.

Further, there is a conventional white light emitting apparatus thatemits white light using the combination of a blue LED and red and greenphosphors having different excitation wavelengths. Since the white lightemitting apparatus has red, green, and blue peak wavelengths, the whitelight emitting apparatus has color rendering and color reproductionproperties superior to a light emitting apparatus using a yellowphosphor. However, in such a light emitting apparatus, different kindsof phosphors are positioned in an encapsulant without being separatedfrom each other. For this reason, light loss may be high, and efficiencyof the phosphors may be degraded.

SUMMARY OF THE INVENTION

The present invention provides a warm white light emitting apparatus inwhich an LED-phosphor combination to generate a base light of white oryellowish white and another LED-phosphor combination to adjust a ColorRendering Index (CRI) of the base light are is employed to simplyprovide high quality warm white light near the BBL curve.

The present invention also provides a warm white light emittingapparatus in which high quality warm white light near the BBL curve maybe simply provided using two LED-phosphor combinations, and analternating current (AC) LED suitable for large-sized electronic displayboards or large-sized monitors as an LED is used in each LED-phosphorcombination to generate a base light.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

Exemplary embodiments of the present invention disclose a warm whitelight emitting apparatus including a first LED-phosphor combination togenerate a base light that is white or yellowish white and a secondLED-phosphor combination to generate a CRI adjusting light. The baselight and the CRI adjusting light together make a warm white lighthaving a color temperature of 2500 to 4500K.

Exemplary embodiments of the present invention also disclose a warmwhite light emitting apparatus including a first combination of at leastone AC LED and at least one kind of phosphor to generate a base lightthat is white or yellowish white and a second combination of at leastone direct current (DC) LED and at least one phosphor to generate a CRIadjusting light. The base light and the CRI adjusting light togethermake a warm white light.

Exemplary embodiments of the present invention also disclose a backlightmodule including a light guide plate, and a warm white light emittingapparatus to supply light to a side surface of the light guide plate.The warm white light emitting apparatus includes an outer wall to definea space in which the first and second LED-phosphor combinations aredisposed and a partition wall to separate the first and secondLED-phosphor combinations from each other. The outer wall is adjacent tothe side surface of the light guide plate, and the partition wall has alower height than the outer wall to be spaced apart from the sidesurface of the light guide plate.

Exemplary embodiments of the present invention further disclose a warmwhite light emitting apparatus including a first combination and asecond combination. The first combination includes a blue LED having apeak wavelength of 400 to 470 nm and at least one phosphor having a peakwavelength of 500 to 600 nm and generates a base light that is white oryellowish white. The second combination includes a blue LED having apeak wavelength of 400 to 470 nm and at least one phosphor having a peakwavelength greater than 600 nm and generates a CRI adjusting light. Thebase light and the CRI adjusting light together make a warm white light.

Exemplary embodiments of the present invention additionally disclose awarm white light emitting apparatus including a first combination and asecond combination. The first combination includes a blue LED having apeak wavelength of 400 to 470 nm and at least one phosphor having a peakwavelength of 500 to 600 nm and generates a base light that is white oryellowish white. The second combination includes an ultra violet (UV)LED having a peak wavelength of 250 to 400 nm and at least one phosphorhaving a peak wavelength greater than 600 nm and generates a CRIadjusting light. The base light and the CRI adjusting light togethermake a warm white light.

Exemplary embodiments of the present invention also disclose a warmwhite light emitting apparatus including a first combination and asecond combination. The first combination includes an AC LED having apeak wavelength in a blue region and at least one phosphor having a peakwavelength of 500 to 600 nm. The second combination includes a DC LEDhaving a peak wavelength in a UV or blue region and at least onephosphor having a peak wavelength greater than 600 nm.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 8 aresectional views of warm white light emitting apparatuses according toexemplary embodiments of the present invention in which a plurality ofLED-phosphor combinations are positioned in a single package.

FIG. 9 and FIG. 10 are circuit diagrams showing examples of AC LEDs ofan LED-phosphor combination to generate a base light among theLED-phosphor combinations of FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5,FIG. 6, FIG. 7, and FIG. 8.

FIG. 11 is a graph showing light emitting characteristics of an AC LEDusing a delay phosphor.

FIG. 12 is a sectional view of a warm white light emitting apparatusincluding LED-phosphor combinations respectively positioned in aplurality of packages according to an exemplary embodiment of thepresent invention.

FIG. 13 and FIG. 14 are sectional views showing backlight modules thateach include a warm white light emitting apparatus according to anexemplary embodiment of the present invention.

FIG. 15 is a view showing regions of base light and CRI adjusting lightdefined by color coordinates on a CIE 1931 chromaticity diagram toobtain warm white light according to an exemplary embodiment the presentinvention.

FIG. 16 is a CIE 1931 chromaticity diagram showing full colors of aconventional warm white light emitting apparatus.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the size and relative sizes oflayers and regions may be exaggerated for clarity. Like referencenumerals in the drawings denote like elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent.

According to a typical classification reference, white light isclassified as warm is white light, pure white light, or cool white lightdepending on the color temperature of the white light. However, the“warm white light” is herein defined as white light except cool whitelight, i.e., white light including typical warm white light and purewhite light. Herein, the term “base light” refers to light that is amaterial of the warm white light to be finally obtained, which has anexcellent color rendering property near a BBL curve.

Light emitting apparatuses according to first, second, and thirdexemplary embodiments of the present invention, in which warm whitelight is provided by two LED-phosphor combinations that each include ablue LED, will be described with reference to FIG. 1, FIG. 2, and FIG.3.

Use of Blue LEDs: First, Second, and Third Exemplary Embodiments

FIG. 1 is a sectional view of a warm white light emitting apparatusaccording to the first exemplary embodiment of the present invention.

As shown in FIG. 1, the warm white light emitting apparatus according tothe first exemplary embodiment of the present invention includes firstand second LED-phosphor combinations 110 and 120, and a housing 130having cavities to accommodate LEDs and phosphors of the combinations.In this exemplary embodiment, the housing 130 includes two cavities 131a and 131 b that are independent of each other. Transparent encapsulants140 a and 140 b to protect LEDs and the like may be formed in thecavities 131 a and 131 b, respectively.

In this exemplary embodiment, the first LED-phosphor combination 110includes a first blue LED 112 and a yellow phosphor 114 corresponding tothe first blue LED 112. Also, the second LED-phosphor combination 120includes a second blue LED 122 and a red phosphor 124 corresponding tothe second blue LED 122. The first and second blue LEDs 112 and 122 havea peak wavelength range of about 400 to 470 nm. For example, the yellowphosphor 114 is provided in the first LED-phosphor combination 110 mayhave a peak wavelength range of about 500 to 600 nm.

In this exemplary embodiment, although the yellow phosphor 114 in thefirst LED-phosphor combination 110 may be a single yellow phosphor, thepresent invention is not limited thereto. That is, two or more kinds ofphosphors having a peak wavelength range of 500 to 600 nm may be used asthe phosphor 114 of the first LED-phosphor combination 110. For example,a phosphor having a peak wavelength range of 500 to 550 nm and aphosphor having a peak wavelength range of 550 to 600 nm may be usedtogether as the phosphor 114 of the first LED-phosphor combination 110.

The first LED-phosphor combination 110 generates base light of white oryellowish white through the combination of blue light emitted from anLED and yellow light emitted from a phosphor. In the first LED-phosphorcombination 110, a portion of blue light emitted from the first blue LED112 excites the yellow phosphor 114. The yellow phosphor 114 can allowblue light to be wavelength-converted into yellow light by theexcitation. The rest of the blue light emitted from the first blue LED112 dose not collide with the yellow phosphor 114 and advances as it is.The base light of white or yellowish white is generated through amixture of the yellow light generated by the wavelength conversion andthe blue light that is not wavelength-converted.

However, since the color rendering property of the base light may beconsiderably degraded, it may be necessary to adjust the CRI.Accordingly, the base light may be mixed with CRI adjusting lightgenerated by the second LED-phosphor combination 120, as describedbelow, in order to generate warm white light near a BBL curve.

The second LED-phosphor combination 120 generates CRI adjusting light,which is mixed with the base light generated from the first LED-phosphorcombination 110. It may be difficult to provide the warm white lightnear the BBL curve using a single LED-phosphor combination. However, thewarm white light near the BBL curve may be generated by the mixture ofthe base light generated by the first LED-phosphor combination 110 andthe CRI adjusting light generated by the second LED-phosphor combination120. A single red phosphor having a peak wavelength range greater than600 nm may be used as the red phosphor 124 of the second LED-phosphorcombination 120.

It is advantageous that the color coordinate range of the base light beas distant from the BBL curve as possible on a CIE 1931 chromaticitydiagram as shown in FIG. 15, i.e., that a Y-coordinate of the CIE 1931chromaticity diagram is large. However, the color coordinate range ofthe base light may be determined to the extent that the color coordinaterange can be drawn near the BBL curve due to the CRI adjusting lighthaving an almost fixed color coordinate range.

The base light generated by the first LED-phosphor combination 110 isdetermined to exist in a first rectangular region defined by colorcoordinates (0.29, 0.45), (0.33, 0.37), (0.52, 0.47), and (0.45, 0.54).The CRI adjusting light generated by the second LED-phosphor combination120 is determined to exist in a second rectangular region defined bycolor coordinates (0.36, 0.34), (0.44, 0.20), (0.67, 0.32), and (0.55,0.44). At this time, the light obtained by the first and secondLED-phosphor combinations 110 and 120 is not cool white light but warmwhite light and exists near the BBL curve. The obtained warm white lightmay have a color temperature range of about 2500 to 4500K, mostpreferably 2500K to 3500K.

The yellow phosphor 114 capable of providing the color coordinate regionof the base light together with the blue LED may include at least one oforthosilicate based yellow, amber, and green phosphors. The yellow andgreen phosphors may be (Ba, Sr, Ca, Cu)₂SiO₄:Eu, and the amber phosphormay be (Ba, Sr, Ca)₂SiO₄:Eu. In addition, various kinds of phosphorssuch as YAG:Ce, Tag-Ce, and Sr₃SiO₅:Eu may be used in the firstLED-phosphor combination 110.

For example, a nitride-based red phosphor, such as (Ca, Sr,Ba)₂Si₅N₈:Eu, (Mg, Ca, Sr)AlSiN₃:Eu, (Ca, Sr, Ba)Si₇N₁₀:Eu, or (Ca, Sr,Ba)SiN₂:Eu, may be used as the red phosphor 124 capable of providing thecolor coordinate region of the CRI adjusting light together with a blueLED or an ultraviolet (UV) LED. For example, CaAlSiN₃:Eu may be used asthe red phosphor 124.

The second LED phosphor combination 120 may be completely separated fromthe first LED-phosphor combination 110 by a partition wall 132 formedbetween the cavities 131 a and 131 b. Accordingly, it may be possible toprevent the phosphors and LEDs of the first and second LED-phosphorcombinations 110 and 120 from operating in exchange for each other untillight is generated by the respective first and second LED-phosphorcombinations 110 ad 120 themselves. Inner wall surfaces of the twocavities 131 a and 131 b may be inclined reflective surfaces. However,inner wall surfaces defined by the partition wall 132 may be vertical orinclined less than the other inner surfaces. Alternatively, thepartition wall 132 may be omitted, and the phosphors of the first andsecond LED-phosphor combinations 110 and 120 may be independentlyseparated from each other in a cluster form, which is also in the scopeof exemplary embodiments of the present invention. Light emitted fromthe LED of one combination may have no influence on the phosphor of theother combination. However, in some exemplary embodiments there may be aslight influence on the phosphor of one combination by light emittedfrom the LED of the other combination.

In this exemplary embodiment, the first and second LEDs 112 and 122belong to the first and second LED-phosphor combinations 110 and 120 andare positioned on the bottom surfaces of the first and second cavities131 a and 131 b, respectively. The yellow phosphor 114 of the firstLED-phosphor combination 110 and the red phosphor 124 of the secondLED-phosphor combination 120 are positioned over the top surfaces of thefirst and second encapsulants 140 a and 140 b independently formed inthe first and second cavities 131 a and 131 b, respectively. Althoughnot shown, the housing 130 may be provided with lead terminals to supplypower to the LEDs 112 and 122.

The phosphors 114 and 124 may be in the form of particles and may becontained in a coating layer or a secondarily molded body formed on thetop surface of the encapsulants 140 a and 140 b. Alternatively, theyellow and red phosphors 114 and 124 may be in the form of particles andmay be contained in a film adhering to the top surface of theencapsulants 140 a and 140 b. Although not shown, the yellow phosphor114 and the red phosphor 124 may be widely scattered in the form ofparticles in the first and second encapsulants 140 a and 140 b,respectively.

As briefly described above, the second LED-phosphor combination 120 maygenerate pink light close to red light, i.e., CRI adjusting light, whichis mixed with the base light generated from the first LED-phosphorcombination 110 to adjust the CRI of the base light. In the secondLED-phosphor combination 120, blue light emitted from the second blueLED 122 excites the red phosphor 124. The red phosphor 124 may generatepink light that is wavelength-converted by the excitation. The pinklight may be used to adjust the color temperature of white light.

Ideally, all light emitted from the second blue LED 122 acts with thered is phosphor 124. However, a portion of blue light emitted from thesecond blue LED 122 may be emitted to the outside as it is. Althoughsuch blue light may be emitted from the second LED-phosphor combination120, the blue light may be mixed with yellow light wavelength-convertedby the yellow phosphor 114 of the first LED-phosphor combination 110 togenerate the aforementioned white light, which means that the emissionof blue light from the second LED-phosphor combination 120 may beunlimited.

FIG. 2 is a sectional view of a warm white light emitting apparatusaccording to the second exemplary embodiment of the present invention.Referring to FIG. 2, the warm white light emitting apparatus accordingto the second exemplary embodiment of the present invention includes afirst LED-phosphor combination 110 having a first blue LED 112 and ayellow phosphor 114 and a second LED-phosphor combination 120 having asecond blue LED 122 and a red phosphor 124, like the previous exemplaryembodiment.

The second exemplary embodiment is different from the previous exemplaryembodiment in that an encapsulant 140 is positioned in a single cavity131 of a housing 130, and the yellow and red phosphors 114 and 124 areformed differently in position and method. In this exemplary embodiment,the yellow and red phosphors 114 and 124 individually cover the firstand second LEDs 112 and 122, respectively. The method of covering an LEDwith a phosphor may include a method of dotting an LED with a liquidresin containing a phosphor, a method using a reflector containing aphosphor, a method of coating an LED with a phosphor throughelectrophoresis, and the like.

In this exemplary embodiment, the first blue LED 112 and the yellowphosphor 114 covering the first blue LED 112 constitute the firstLED-phosphor combination 110 to generate base light of white oryellowish white, and the second blue LED 122 and the red is phosphor 124covering the second blue LED 122 constitute the second LED-phosphorcombination 120 to generate pink light for CRI adjustment.

FIG. 3 is a sectional view of a warm white light emitting apparatusaccording to the third exemplary embodiment of the present invention.Like the previous exemplary embodiment, the warm white light emittingapparatus according to the third exemplary embodiment of the presentinvention includes a first LED-phosphor combination 110 having a firstblue LED 112 and a yellow phosphor 114 and a second LED-phosphorcombination 120 having a second blue LED 122 and a red phosphor 124, andboth of the first and second LED-phosphor combinations 110 and 120 arepositioned in a single cavity 131 of a housing 130.

The third exemplary embodiment is different from the previous exemplaryembodiment in that only the second blue LED 122 of the secondLED-phosphor combination 120 is individually covered with the redphosphor 124, and the blue LED 112 of the first LED-phosphor combination110 is encapsulated with only an encapsulant 140. The yellow phosphor114 of the first LED-phosphor combination 110 is provided on the topsurface of the encapsulant 140 or inside of the encapsulant 140. In thisexemplary embodiment, the encapsulant 140 encapsulates both of the redphosphor 124 and the second blue LED 122 covered with the red phosphor124 as well as the first blue LED 112.

According to this exemplary embodiment, in first LED-phosphorcombination 110, a portion of blue light emitted from the first LED 112is wavelength-converted into yellow light by the yellow phosphor 114positioned on the top surface of the encapsulant 140 (or inside of theencapsulant 140), and the rest of the blue light is mixed with theyellow light without wavelength conversion, thereby generating baselight of white or yellowish white. In the second LED-phosphorcombination 120, a large amount of blue light emitted from the second isblue LED 122 is converted into pink light, which is used to adjust thecolor temperature of white light, by the red phosphor 124 directly andindividually covering the second blue LED 122. At this time, since theyellow phosphor 114 has an energy level much higher than that of the redphosphor 124, light emitted by exciting the red phosphor 124 may havesubstantially no influence on the yellow phosphor 114. Accordingly, onlythe second LED 122 may be individually covered with the red phosphor124.

Hereinafter, a warm white light emitting apparatus according to a fourthexemplary embodiment, in which a UV LED is partially used, will bedescribed with reference to FIG. 4.

Use of Blue LED and UV LED: Fourth Exemplary Embodiment

FIG. 4 is a sectional view of a warm white light emitting apparatusaccording to the fourth exemplary embodiment of the present invention.Referring to FIG. 4, the warm white light emitting apparatus accordingto the fourth exemplary embodiment of the present invention includes afirst LED-phosphor combination 110 having a blue LED 112 and a yellowphosphor 114, and a second LED-phosphor combination 120′ having a UV LED122′ and a red phosphor 124′. Both of the first and second LED-phosphorcombinations 110 and 120′ are positioned in a single cavity 131 of ahousing 130. The blue LED 112 and the UV LED 122′ are individuallycovered with the yellow phosphor 114 and the red phosphor 124′,respectively. An encapsulant 140 encapsulates all of the elements of thefirst and second LED-phosphor combinations 110 and 120′. Here, in thesecond LED-phosphor combination 120′, the red phosphor 124′ may have apeak wavelength range greater than 600 nm and the UV LED 122′ may have apeak wavelength range of 250 to 400 nm.

Although not specifically shown, the structure in which the first andsecond LED-phosphors are separated from each other may be variouslymodified as long as a UV LED is used in the second LED-phosphorcombination to generate CRI adjusting light (see FIGS. 1, 12, 13, and14).

Hereinafter, warm white light emitting apparatuses according to fifth,sixth, seventh, and eighth exemplary embodiments of the presentinvention, wherein an AC LED is used as a blue LED in a firstLED-phosphor combination to generate base light, will be described withreference to FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, and FIG.11.

Use of AC LED: Fifth, Sixth, Seventh, and Eighth Exemplary Embodiments

FIG. 5 is a sectional view of a warm white light emitting apparatusaccording to the fifth exemplary embodiment of the present invention.Referring to FIG. 5, the warm white light emitting apparatus accordingto the fifth exemplary embodiment of the present invention includes afirst LED-phosphor combination 110 and a plurality of secondLED-phosphor combinations 120, which are positioned in a single packagehousing 130. At this time, the plurality of second LED-phosphorcombinations 120 is disposed around the first LED-phosphor combination110. In this exemplary embodiment, base light of white or yellowishwhite, which is generated from the first LED-phosphor combination 110,is equally mixed with CRI-mixed light generated from the plurality ofsecond LED-phosphor combinations 120 disposed around the firstLED-phosphor combination 110. Accordingly, the combinations 110 and 120may generate uniform warm white light without color variation.

The first blue LED 112 of the first LED-phosphor combination 110 may bean AC LED operated by AC current. FIG. 5 is an enlarged view of theconfiguration of an AC LED chip. Referring to the enlarged view, the ACLED chip is formed by growing semiconductor layers on a substrate 112-1.The AC LED chip includes a plurality of light emitting cells C₁, C₂, . .. , C_(n-1), and C_(n) connected in series through wires W₁, W₂, . . .W_(n-1), and W_(n).

Each light emitting cell C₁, C₂, . . . , C_(n-1), and C_(n) includes ann-type semiconductor layer 1121, an active layer 1122, and a p-typesemiconductor layer 1123, which are sequentially formed on the substrate112-1 or a buffer layer (not shown) formed on the substrate 112-1. Atthis time, a transparent electrode layer 112-2 may be formed on thep-type semiconductor layer 1123. Further, a portion of the active layer1122 and the p-type semiconductor layer 1123 is removed in a region ofthe n-type semiconductor layer 1121, so that an electrode may beprovided in the region of the n-type semiconductor layer 1121. Forexample, the electrode may be connected to a p-type semiconductor layerof an adjacent light emitting cell through the wire.

The wire W₁ connects the n-type semiconductor layer 1121 of the lightemitting cell C₁ to the electrode of the p-type semiconductor layer 1123of another adjacent light emitting cell C₂. A serial array of theplurality of light emitting cells may be connected in reverse parallelwith a serial array of other light emitting cells formed on the samesubstrate.

As described above, the AC LED 112 may be formed by growing an n-typesemiconductor layer, an active layer, and a p-type semiconductor layeron a substrate, dividing the semiconductor layers into a plurality oflight emitting cells C₁, C₂, . . . , C_(n-1), and C_(n), and thenconnecting the light emitting cells in series or parallel.Alternatively, the AC LED may be formed by mounting a plurality ofprefabricated LED chips on a submount and then connecting the pluralityof LED chips mounted on the submount in series or parallel. In thiscase, a material of the submount may include any one of AlN, Si, Cu,Cu—W, Al₂O₃, SiC, ceramic, and the like. If necessary, a material toisolate the submount from each LED chip may be disposed between thesubmount and each LED chip.

Meanwhile, since an AC LED connected to an AC power source is repeatedlyis turned on/off depending on a direction of current, the flickeringphenomenon where light emitted from the AC LED flickers occurs. Here, ifa DC LED operated by DC current is used as an LED 122 of each secondLED-phosphor combination 120, flickering may be reduced. In order tofurther reduce flickering and total harmonic distortion (THD), ananti-coupling circuit unit and/or an anti-THD circuit unit may beconnected in the form of a device or IC to an AC LED or an operationcircuit thereof. Further, a current control unit, which controls currentflowing through the AC LED to be different depending on a change intemperature of the AC LED and/or the DC LED, may be connected to theoperation circuit of the AC LED.

FIG. 6 is a sectional view of a warm white light emitting apparatusaccording to the sixth exemplary embodiment of the present invention,and shows the warm white light emitting apparatus, which furtherincludes an additional circuit unit 150 to reduce flickering or the likein a package. The circuit unit 150 may be an anti-flickering circuitunit to reduce flickering or an anti-THD circuit unit to reduce THD. Thecircuit unit 150 is connected to a lead terminal (not shown) connectedto an AC LED 112 of a first LED-phosphor combination 110. Theanti-flickering circuit unit and/or the anti-THD circuit unit may beembedded in a package together with the circuit unit 150 shown in FIG.6, or may be connected to the AC LED 112 at the outside of the package.A DC LED 122 of a second LED-phosphor combination 120 may be connectedto an electric circuit independent from a power source of the AC LED112, or may be connected to an additional circuit unit to improveperformance of the DC LED.

FIG. 7 is a sectional view of a warm white light emitting apparatusaccording to the seventh exemplary embodiment of the present invention.Referring to FIG. 7, the warm white light emitting apparatus accordingto this exemplary embodiment includes a layer 190 containing a delayphosphor (hereinafter, referred to as a “delay phosphor layer”). Thedelay is phosphor layer 190 may reduce the flickering of an AC LED 112.An encapsulant 140, which encapsulates both the first and secondLED-phosphor combinations 110 and 120, may be made of a silicon or epoxymaterial and is coated with the delay phosphor layer 190.

The delay phosphor may be a silicate phosphor, an aluminate phosphor, asulfide phosphor, or the like disclosed in U.S. Pat. Nos. 5,770,111,5,839,718, 5,885,483, 6,093,346, and 6,267,911, which are all herebyincorporated by reference. For example, the delay phosphor may be (Zn,Cd)S:Cu, SrAl₂O₄:Eu, Dy, (Ca, Sr)S:Bi, ZnSiO₄:Eu, (Sr, Zn, Eu, Pb,Dy)O.(Al, Bi)₂O₃, m(Sr, Ba)O.n(Mg, M)O.2(Si, Ge)O₂:Eu, Ln, or the like,where 1.5≦m≦3.5, 0.5≦n≦1.5, M may be at least one element selected fromthe group consisting of Be, Zn, and Cd, and Ln may be at least oneelement selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm,Gd, Tb, Dy, Ho, Er, Tm, Yb, K, Lu, B, Al, Ga, In, Tl, Sb, Bi, As, P, Sn,Pb, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cr, and Mn. The delay phosphor isexcited by a portion of light generated from the first and secondLED-phosphor combinations 110 and 120 and then emits light in a visiblelight region, e.g., red, green, and/or blue light.

The decay time of the delay phosphor may be 1 msec or more, morepreferably 8 msec or more. The maximum decay time of the delay phosphormay vary depend on the use of the light emitting apparatus. Although themaximum decay time of the delay phosphor is not specifically limited, itmay be 10 hours or less.

Unlike the previous exemplary embodiment, a delay phosphor may beindependently applied to a first LED-phosphor combination 110 and/or asecond LED-phosphor combination 120, which is shown in FIG. 8( a) andFIG. 8( b) according to the eighth exemplary embodiment of the presentinvention.

Referring to FIG. 8( a), delay phosphor layers 191 a and 191 b may bedirectly is formed on respective surfaces of an AC LED 112 of the firstLED-phosphor combination 110 and a DC LED 122 of the second LED-phosphorcombination 120 by an electrophoresis method, for example. Referring toFIG. 8( b), delay phosphor layers 192 a and 192 b may be directly formedon respective surfaces of a resin portion containing a general yellowphosphor 114 of the first LED-phosphor combination 110 and a resinportion containing a general red phosphor 124 of the second LED-phosphorcombination 120. Alternatively, a delay phosphor may be contained in theresin portions of the first and second LED-phosphor combinations 110 and120 or only in the resin portion of the first LED-phosphor combination110.

FIG. 9 and FIG. 10 are circuit diagrams showing examples of AC LEDs,which may be used in the aforementioned first LED-phosphor combination.FIG. 11 is a graph showing the effect of the aforementioned delayphosphor.

Referring to FIG. 9, light emitting cells C₁, C₂, and C₃ of an AC LEDare connected in series to form a first serial light emitting cellarray, and the other light emitting cells C₄, C₅, and C₆ are connectedin series to form a second serial light emitting cell array. Here, the“serial light emitting cell array” refers to an array of a plurality oflight emitting cells connected in series. Both ends of each of the firstand second serial light emitting cell arrays are connected to an ACpower source 35 and a ground through lead terminals, respectively. Thefirst and second serial arrays are connected in reverse parallel betweenthe AC power source 35 and the ground. Therefore, when the AC powersource 35 has a positive phase, the light emitting cells C₁, C₂ and C₃constituting the first serial light emitting cell array are turned on.When the AC power source 35 has a negative phase, the light emittingcells C₄, C₅, and C₆ constituting the second serial light emitting cellarray are turned on.

Referring to FIG. 10, light emitting cells C₁, C₂, C₃, C₄, C₅, and C₆constitute a is serial light emitting cell array, and a bridge rectifierincluding diode cells D₁, D₂, D₃, and D₄ is disposed between an AC powersource 35 and the serial light emitting cell array and between a groundand the serial light emitting cell array. An anode terminal of theserial light emitting cell array is connected to a node between thediode cells D₁ and D₂, and a cathode terminal of the serial lightemitting cell array is connected to a node between the diode cells D₃and D₄. A terminal of the AC power source 35 is connected to a nodebetween the diode cells D₁ and D₄, and the ground is connected to a nodebetween the diode cells D₂ and D₃. When the AC power source has apositive phase, the diode cells D₁ and D₃ are turned on, and the diodecells D₂ and D₄ are turned off. Therefore, current flows to the groundvia the diode cell D₁, the serial light emitting cell array, and thediode cell D₃. On the other hand, when the AC power source 35 has anegative phase, the diode cells D₁ and D₃ are turned off, and the diodecells D₂ and D₄ are turned on. Therefore, current flows to the AC powersource via the diode cell D₂, the serial light emitting cell array, andthe diode cell D₄.

The dotted curve of FIG. 11 shows a light emitting characteristic of alight emitting apparatus having an AC LED without a delay phosphor,while the solid curve of FIG. 11 shows a light emitting characteristicof a light emitting apparatus having an AC LED including a delayphosphor. Here, a DC LED included in the light emitting apparatus isintentionally not operated.

Referring to FIG. 11, when the delay phosphor is not used, the lightemitting apparatus is periodically turned on/off when AC voltage isapplied thereto. Assuming that a period of the AC voltage is T, twoarrays of light emitting cells connected in series alternately operateonce during a period of T. Therefore, the light emitting apparatus emitslight every period of T/2, as indicated by the dotted curve. When the ACvoltage does not exceed the is threshold voltage of the light emittingcells connected in series, the light emitting cells do not operate.Therefore, the light emitting cells are in an off state for a certainperiod between times at which the light emitting cells operate, i.e., aperiod when the AC voltage is smaller than the threshold voltage of thelight emitting cells. Accordingly, the AC LED may cause flickering tooccur in the light emitting apparatus due to the interval between thetimes at which the light emitting cells operate.

When the delay phosphor is used, light is still emitted while the lightemitting cells are turned off, as indicated by the solid curve.Therefore, although light intensity may be varied, the time when lightis not emitted may be shortened. If the decay time of the delay phosphoris long, the light emitting apparatus may continuously emit light. Whena general household AC power source applies voltage having a frequencyof about 60 Hz, one cycle of the power is about 16.7 msec, and a halfcycle of the power is about 8 msec. Therefore, while the light emittingapparatus operates, the time when the light emitting cells are allturned off is shorter than 8 msec, so that when the decay time of thedelay phosphor is 1 msec or more, flickering may be sufficientlyreduced. Particularly, when the decay time of the delay phosphor issimilar to the time when the light emitting cells are all turned off,the light emitting apparatus may continuously emit light.

The delay phosphor may be further provided in addition to the phosphorsof the aforementioned first and second LED-phosphor combinations.Alternatively, the phosphors of the first and second LED-phosphorcombinations may be replaced by delay phosphors.

The warm white light emitting apparatuses having a structure in whichfirst and second LED-phosphor combinations are all positioned in asingle package have been described in the previous exemplaryembodiments. On the other hand, a warm white light emitting is apparatusaccording to a ninth exemplary embodiment of the present invention,shown in FIG. 12, has a structure in which first and second LED-phosphorcombinations are positioned in different packages, respectively.

Use of Plurality of Packages: Ninth Exemplary Embodiment

Referring to FIG. 12, the warm white light emitting apparatus accordingto the ninth exemplary embodiment of the present invention comprises aframe 200 having a base portion 210 and a reflective portion 220. Afirst package 231 is positioned on a central portion of the top surfaceof the base portion 210, and a plurality of second packages 232 arepositioned around the first package 231. A first LED-phosphorcombination 110 to generate base light of white or yellowish white isincluded in the first package 231, and a second LED-phosphor combination120 to generate CRI adjusting light is included in each of secondpackage 232.

As in the previous exemplary embodiments, the first LED-phosphorcombination 110 includes an AC LED 112 to emit blue light and one ormore phosphors 114 having a peak wavelength of 500 to 600 nm. The secondLED-phosphor combination 120 includes a blue or UV LED 122 and one ormore phosphors 124 having a peak wavelength greater than 600 nm.

An anti-flickering circuit unit 152 and/or an anti-THD circuit unit 154may be installed on the base portion 210. Also, the base portion 210 maybe provided with a circuit 156, which has various components including aheat dissipation system, a ballast, a driver, and/or a driving circuit.The reflective portion 220 reflects a portion of light generated fromthe first and second LED-phosphor combinations 110 and 120, in which adelay phosphor layer 193, which reduces flickering of an AC LED, isformed on an inner surface of the reflective portion 220.

Hereinafter, backlight modules that include a warm white light emittingapparatus is according to an exemplary embodiment of the presentinvention will be described with reference to FIG. 13 and FIG. 14.

Backlight Module

Referring to FIG. 13, the backlight module includes a light guide plate30 and a light emitting apparatus 10 to supply light to the light guideplate 30. The light emitting apparatus 10 is adjacent to a side surfaceof the light guide plate 30 and includes an outer wall 132 toaccommodate first and second LED-phosphor combinations 110 and 120therein. A partition wall 134 to separately accommodate the first andsecond LED-phosphor combinations 110 and 120 is formed in a cavitydefined by the outer wall 132. The height of the partition wall 134 islower than that of the outer wall 132. Therefore, a region in which baselight of white or yellowish white generated from the first LED-phosphorcombination 110 may be mixed with pink CRI adjusting light generatedfrom the second LED-phosphor combination 120 is provided adjacent to theside surface of the light guide plate 30.

A first blue LED 112 is positioned at the left side of the partitionwall 134, and a flat first phosphor resin layer L1, which covers thefirst blue LED 112 and contains one or more phosphors 114 having a peakwavelength of 500 to 600 nm, is formed to a height lower than that ofthe partition wall 134. In addition, a second blue LED 122 is positionedat the right side of the partition wall 134, and a flat second phosphorresin layer L2, which covers the second blue LED 122 and contains one ormore phosphors 124 having a peak wavelength greater than 600 nm, isformed to a height lower than that of the partition wall 134. Atransparent resin layer T is formed to cover the first and secondphosphor resin layers L1 and L2. The transparent resin layer T may havethe same height as the outer wall 132 to be in contact with the side ofthe light guide plate 30.

The backlight module shown in FIG. 14 includes a light emittingapparatus 10 having a partition wall 134, which is smaller than an outerwall 132. First and second LED-phosphor combinations 110 and 120 areseparated by the partition wall 134. However, this backlight module isdifferent from the backlight module of the previous exemplary embodimentin that resin portions containing phosphors 114 and 124 of thecombinations 110 and 120 are formed in a hemispherical shape and thetransparent resin layer T is omitted. Each hemispherical resin portion,in which phosphors 114 and 124 of the first and second LED-phosphorcombinations 110 and 120 are respectively contained, has a height lowerthan that of the outer wall 132.

According to exemplary embodiments of the present invention, warm whitelight having a high color rendering property near a BBL curve, which maybe difficult for a conventional LED-phosphor combination to provide, maybe simply provided by employing a first LED-phosphor combination togenerate base light of white or yellowish white and a secondLED-phosphor combination to generate CRI adjusting light to allow thebase light to be drawn near the BBL curve.

According to exemplary embodiments of the present invention, highquality warm white light near a BBL curve may be simply provided usingtwo LED-phosphor combinations. An AC LED is used as an LED of theLED-phosphor combination to generate the base light, thereby providing awarm white light emitting apparatus suitable for a large-sizedelectronic display board or large-sized monitor. Further, a DC LED maybe used as an LED of the LED-phosphor combination to generate the CRIadjusting light, whereby flickering of the warm white light emittingapparatus may be reduced. Furthermore, a delay phosphor, ananti-flickering circuit unit, and/or an anti-THD circuit unit may befurther provided in the warm white light is emitting apparatus so thatflickering and/or THD of the AC LED may be further reduced.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A warm white light emitting apparatus, comprising: a firstcombination of at least one alternating current (AC) light emittingdiode (LED) and at least one phosphor to generate a base light, the baselight being white or yellowish white; and a second combination of atleast one direct current (DC) LED and at least one phosphor to generatea Color Rendering Index (CRI) adjusting light, wherein the base lightand the CRI adjusting light together make a warm white light.
 2. Thewarm white light emitting apparatus of claim 1, wherein the warm whitelight has a color temperature of 2500 to 4500K.
 3. The warm white lightemitting apparatus of claim 1, wherein the base light exists in arectangular region defined by color coordinates (0.29, 0.45), (0.33,0.37), (0.52, 0.47), and (0.45, 0.54) on a Commission on Illumination(CIE) chromaticity diagram, and the CRI adjusting light exists in arectangular region defined by color coordinates (0.36, 0.34), (0.44,0.20), (0.67, 0.32), and (0.55, 0.44) on the CIE chromaticity diagram.4. The warm white light emitting apparatus of claim 1, wherein in thefirst combination, the at least one AC LED comprises a blue LED, and theat least one phosphor has a peak wavelength of 500 to 600 nm.
 5. Thewarm white light emitting apparatus of claim 1, wherein in the secondcombination, the at least one DC LED comprises a blue LED or anultraviolet (UV) LED, and the at least one phosphor has a peakwavelength greater than 600 nm.
 6. The warm white light emittingapparatus of claim 1, wherein the at least one AC LED comprises aplurality of connected light emitting cells, the light emitting cellsrespectively comprising semiconductor layers on a single substrate. 7.The warm white light emitting apparatus of claim 1, wherein the at leastone AC LED comprises a plurality of connected LED chips, which aremounted on a single submount.
 8. The warm white light emitting apparatusof claim 1, wherein at least one of the first combination and the secondcombination further comprises a delay phosphor.
 9. The warm white lightemitting apparatus of claim 1, further comprising a delay phosphorcontained in an encapsulant, the encapsulant encapsulating both of thefirst combination and the second combination.
 10. The warm white lightemitting apparatus of claim 1, wherein the first combination and thesecond combination are positioned in different packages, respectively.11. The warm white light emitting apparatus of claim 10, furthercomprising a frame comprising a base portion having the differentpackages mounted thereon and a reflective portion to reflect lightgenerated from the first combination and the second combination, whereinthe reflective portion comprises a delay phosphor.
 12. The warm whitelight emitting apparatus of claim 1, further comprising ananti-flickering circuit unit connected to the AC LED.
 13. The warm whitelight emitting apparatus of claim 1, further comprising an anti-totalharmonic distortion (THD) circuit unit connected to the AC LED.
 14. Awarm white light emitting apparatus, comprising: a first combination ofan alternating current (AC) light emitting diode (LED) having a peakwavelength in a blue region and at least one phosphor having a peakwavelength of 500 to 600 nm; and a second combination of a directcurrent (DC) LED having a peak wavelength in an ultraviolet (UV) or blueregion and at least one phosphor having a peak wavelength greater than600 nm.
 15. The warm white light emitting apparatus of claim 14, furthercomprising a delay phosphor.
 16. The warm white light emitting apparatusof claim 14, further comprising at least one of and an anti-totalharmonic distortion (THD) circuit unit and an anti-flickering circuitunit.
 17. The warm white light emitting apparatus of claim 14, whereinthe AC LED and the DC LED are individually driven.
 18. The warm whitelight emitting apparatus of claim 14, wherein the first combination andthe second combination are disposed in a single package independently ofeach other.
 19. The warm white light emitting apparatus of claim 14,wherein the first combination and the second combination arerespectively positioned in corresponding cavities divided by a partitionwall in a single package.
 20. The warm white light emitting apparatus ofclaim 14, wherein the corresponding phosphors in the first combinationand the second combination are provided to individually cover thecorresponding LEDs in the first combination and the second combination,respectively.
 21. The warm white light emitting apparatus of claim 14,wherein the first combination and the second combination are containedin different packages, respectively.
 22. The warm white light emittingapparatus of claim 21, further comprising a frame comprising a baseportion having the different packages mounted thereon and a reflectiveportion to reflect light generated from the first combination and thesecond combination.